Ternary alloys of uranium, columbium, and zirconium



Un te TERNARY ALLOYS F URANIUM, 'COLUMBIUM,

AND ZIRCONIUM No Drawing. Filed Sept. 13, 1948, Ser. No. 49,128 12.Claims. 75-1217) This invention relates to ternary alloys "and particularly to ternary alloys of uranium useful as neutron-reflecting materials in a fast neutron pile, which alloys are especially resistant to corrosion'caused by'oxidative processes of aqueous or gaseous origin.

During the course of the investigation of the problem of the susceptibility of uranium metal to oxidative corrosion, it has been discovered that uranium metal in the gamma phase has greater resistance to corrosion by oxidation.

It is therefore an object of this invention to provide compositions of uranium which are resistant to corrosion, and particularly compositions of uranium wherein at least a portion of said uranium is in the corrosion resistant gamma phase.

It is a further object of this invention to provide materials for use in neutronic reactors which necessarily consist predominantly of uranium metal and have the necessary characteristics with respect to neutron capture cross-sections. This object is attained most satisfactorily by alloying uranium metal with materials which will im- Statcs atentO part the desired corrosion resistance to the uranium metal without adversely affecting the nuclear characteristics of the uranium metal.

It is thus a further object of this invention to provide compositions of uranium having a minimum total alloy content and yet attain maximum resistance to corrosion in said uranium materials.

A still further object of this invention is to provide a process for the preparation of the above-mentioned materials which have the desired physical and nuclear prop erties.

Further objects and advantages of this invention will be apparent from further examination of the specifica tion.

In accordance with the subject matter of this invention it has been discovered that uranium metal becomes stabilized in the gamma phase when closely alloyed with minor amounts of columbium and zirconium. I 1

Such alloys, which are predominantly uranium having columbium and zirconium as minor alloying materials, have been found to possess properties superior to those found in binary alloys of uranium wherein the uranium metal is alloyed with either columbium or zirconium alone. In order to stabilize uranium metal in the noncorrodible gamma phase, only small percentages of these minor alloy materials, preferably at least about two percent by weight, have been found to be effective. In fact, the ternary alloys which are predominantly uranium and contain a minimum of about two percent by weight of total alloy material, namely, zirconium and colum bium, have been found to be superior to those binary alloys of uranium and zirconium or uranium and columiable' means such as rollingor extrusion, ;sinice the rate From among those ternary alloysof uranihm having a total alloy content of. columbium and zirconium, those having a total alloy content wherein the ratio of columbium to zirconium is at least approximately 2 to l are preferred since they show greater resistance to corrosion. A total alloy contentr-anging from two per cent to eight percent by weight is suitable for mostpurposes, however, the alloy consisting predominantly of uranium metal alloyed with as little as two percent by total weight of the alloying materials columbium and zirconium wherein the ratio of columbium to zirconium is approximately 2 to 1 is superior with respect to corrosion resistance to those containing a greater total alloy content.

Throughout this specification, by the term fresistance to corrosion is meant that an alloy can Withstand tern peratures between 150 and 200 C. during exposure either to boiling water or to air at a speed of about 150 feet per second. In practice most of these alloys will be sub jected to conditions such that the temperature and air speed would not usually exceed C. and feet per second, respectively, and for this purpose I have found that an alloy may be deemed satisfactory when the corrosion rate. after 500 hours in test is not in excess of .01 mg./cm. /hr. a

As noted before, I have found that uranium metal cast in the high temperature gamma phase shows greater resistance to corrosion than in any other phase. While I do not wish to be bound by any theory as to the mechanism of corrosion, it is perhaps worthy of note that corrosion of uranium metal is attributed to the transformation of uranium metal in the gamma phase to a less corrosion-resistant phase. It is also possible that the gamma phase becomes progressively less corrosionresistant directly with anincrease in temperature, particu larly at temperatures in excess of 200 C. It appears, therefore, that the addition to uranium of between two and eight percent by weight of the minor alloying elements, columbium and zirconium, servesto stabilize the uranium metal in the corrosion-resistant gamma phase either by retarding the inception of corrosion, that is, by extending the threshold level or time necessary for the metal to be affected by oxidation; or, after the threshold has been attained, by reducing the rate of oxidation which has begun. It has been noted that columbium is more effective than zirconium in imparting to uranium metal a greater threshold value and also reducing the rate of oxidation once this threshold has been attained.

In accordance withvthis invention, the process for preparing the ternary alloys comprising the subject matter of this invention comprises casting uranium metal at an i elevated temperature, suitably at about 1000 C., with the desired total weight percent of minor alloy materials, namely, columbium and zirconium. The metallic mixture formed thereby contains uranium metal, at least a portion of which is in the g-amma phase'on account of the elevated casting temperature, with the minor alloying constituents in solid solution of uranium in the as-cast form. In order to homogeuize thismetallicsolution mix- --ture, the alloy mixture is subjected to-a solution heat "i treatment consisting of an extended heating at'a temperature of about 1000 C. for a period ranging from about 60 metals is then either quenched immediately or first-soaked 300 hours to 768 hours. The homogeneous mixture of at a temperature of 850 C. which is thenlfollowed by either rapid or slow quenching. However, ithasbeen noted that the amount of gamma phaseretainedin the uranium material is {favored considerably by'an increase in the, quenching rate which is suitably achieyedby reducing the cross-sectional area of the metal by any-suitof quenching, in the metalunder treatment, increases directly with the reduction in cross-sectional area. Preservation of uranium metal in the gamma phase by alloying with columbium iqairs siaaeaalfis. 2 9

Palzented Aug. 2 1960 a 3 certain when the alloys are prepared according to the process set forth herein.

The superiority of the ternary alloys comprising the subject matter of this invention will be apparent from the binary and ternary alloy samples which had been in the oven for a total of 785 hours, and the samples were cleaned as before in 30% nitric acid and the weight losses measured. Results of these tests showed that pure following descriptions and tables wherein the composi- 6 uranium begins to oxidize as soon'as it is put under test tion, heat treatment and conditions of test are set forth. and proceeds at a constant rate corresponding to a loss An alloy sample which averaged 0.4 we gh Percent of about 0.66 mg./cm. /hr., which corrosion rate is conzirconium and 2.17 weight percent columbium and the siderably reduced by very low alloy additions of colum balance uranium metal was rolled to a it-inch rod at bium, zirconium, or mixtures thereof. Slightly larger 850 C. Specimens of this sample were sub ected to a 10 additions cause the alloy to remain stable until a threshdynamic air corrosion test for 1300 hours where n the old is reached and further additions of alloy extend the air speed to which the specimens were sub ected was length of time before the threshold is attained and reabout 100 feet per second and the temperature was duce the oxidation rate thereafter. 150 C. The weight gain rate for seven specimens The binary uranium alloy containing 0.9% columbium varied from 0.0006 to 0.0018 mg/cmF/hr. The average was approximately as good as the 2.5%-zirconium binary weight gain of 0.0014 mg./cm. /hr. was attained after uranium alloy, both having thresholds at approximately 500 hours. The alloy was then treated with 30% 50 to 60 hours. The binary uranium-4,2% columbium nitric acid to remove any oxide formed during the t alloy had a threshold of 180 to 200 hours and thereafter and the resultant weight loss was plotted against time gained weight very slowly. The binary uranium alloy to obtain a value for the total weight of uranium conontaining 11% l biu d th ternary iu verted to oxide. These figures showed the average rate alloys containing 2% columbium-1% zirconium, and 3% of uranium metal oxidized was 0.008 mg./cm. /h1'. columbium-l% zirconium showed hardly detectable which indicates that the range of weight gain quoted thresholds. The threshold for the alloy of uranium conabove is equivalent to 0.0035 to 0.010 mg./cm. /hr. as taining 2% columbium-1% zirconium was roughly 300 an average rate of oxidation of metal from metal surhour d after a total of 785 hours in test, the alloy faces. had been oxidized at an average rate of 0.005 In a further investlgation of the uranium-columbrummg/omF/hr. at 150 C. At the end of the test it was zirconium system, specimens of binary uranium-columcoated with a uniform thin tenacious film. The -folbium and uranium-zirconium alloys were homogemzed lowing tables further illustrate the relative elficiency of for one week at 1000 C. then soaked at 850 C. f01- different percentages of columbium and zirconium in lowed by a fast bflne q The Samples W61? gFOIlIld eifecting improvements in the physical properties such on g emery P p the total Surface areas mea$- as resistance to corrosion and hardness values in uranium ured and initial weights noted. Each sample was placed metaL in a water glass to collect all the oxide formed and sam- TABLE I ples were then placed in an oven at 150 C. with slow air circulation. Results of this test are shown by the Rockwell C values of U CZ7Z" alloys 'n d f r e fiv most active s ecifouowmg data obtal e 0 th e p Alloy Composition (Nominal 111E118. wt. added to U) Percent Cb 2 2 2 4 4 6 Hours in 40 Percent Zr 2 4 6 2 4 2 Nominal wt. Testin Wt. change, Remarks percent alloy 10.551; a6 mgJemfi/hr. Alloy Treatment:

' Homogenized 768 hrs. at

1,000h and water 3 31 3? 20 2O 90 quenc 0 J d 32% Fairgmconstant rate 'Homogenized 768 hrs. at 282 0.25 Threshold reached corrosion g g. soaked after hrs 50 O. for 256 hrs., err- 282 not detd. Threshold after hrs. 53 53 52 46 y 21 282 0.17 Fairlyconstant rate gain. fi ggg g g gg g 6000- 282 ggggi gg g f reached o. fOI 64 hgs.,tai{-8 .)8le% 30 30 a1 30 so as omogcnize a 282 not detd. Threshold reached at 120 hrs. 50 for 768 hrsqheated at 600 C. for 256 hrs., air-cooled- 35 31 33 30 31 The procedure for the previous test was repeated using TABLE II Percent by wt. Alloy Material (Remaining Percent Uranium) Time in Wt. Change,

Heat Treatment 'Ifiest, Mg./cm. /hr. Remarks I'S. Nominal Actual Pure Uranium Slug Metal (As'cast).- 110 2. 3 Fairly consistent rate.

* Slow-coole a d Wor e 310 .77 Work sample corroded faster at first. D0 Slow-cooled and Unworked 310 77 A fast corrosion rate at beginning of test.

2 Ch. 2 As-cast Furnace-cooled- 540 29 Inconsistent rate.

4 Ob 4; do 562 17 Insignificant wt. change first 230 hrs.

4 Cb..- 4. H.I., 5.5 days at 1,000 0., W.Q 1, 708 001 Most wt. change first 200 hrs.

9 Cb'-- 10.2 Ob As-cast Furnace-cooled 1, 081 0007 9 Cb--. 10.4 Ob H.T., 11 days at 1,000 0., W.Q- 1,708 +.0005 Most wt. change first 200 hrs.

20 Ch 24.8 Cb As-cast Furnace-cooled 5630 none 20 0b-- 23.2 Cb H T 11 days at 1,000 O W Q- 1, 708 none 2 Zr' 1.9 Zr As-cast 264 53 Consistent rate.

2 Zr 1.9 Zr H.T., 18 hrs. at 850 C. W.Q 849 41 Fairly consistent rate.

2 Zr 1.9 Zr H.T., 53 hrs. at 1,000 W.Q 130 71 Sample fell apart.

4.1 Zr- 4.3 Zr As-cast 398 02 Oorroded slowly first hrs.

4.1 Zr- 4.3 Zr H.I., 18 hrs. at 850 C. 994 .007 Consistent rate.

4.1 Zr- 4.3 Zr H.T., 53 hrs. at 1,000 6 919 007 Do.

8 Zr-.. 8.7 Zr As-cast 400 65 Do.

8 Zr- 8.7 Zr H.T., -18 hrs. at 850 C. 991 17 Corroded very slowly first hrs.

2Zr;20b H.T.,l00 hrs. at1,000d.,W.Q was none 4 Zr; 2 0b.. .....do 733 0007 No wt. change first 240 hrs.

6 Zr; 2 0b-. 733 -.-.00056 N 0 wt. change first 400 hrs. This alloy is the least stable since a tester quenching rate was refi uired to retain completely the gamma p ase.

See footnotes at end of table.

TABLE lI-Continued Percent by wt. Alloy Material (Remaining Percent Uranium) Time in Wt. Change,

Heat Treatment 'fiest, MgJcmfl/hr. Remarks rs. Nominal Actual 2 Zr; 4 Oh. H.T., 100 hrs. at 1,000 0., W.Q 733 00014 +0.2 mg. wt. change. 4 Zr; 4 Ch. 733 0002 D0. 2 Zr; 6 Cb 733 none 2 Zr; 2 C H.T., 256 hrs. at 850 0., Air-cooled 446 0004 +0.3 mg. wt. change. 4 Zr; 2 b-- do 446 0003 +0.2 mg. wt. change. 6 Zr; 2 Ch 446 0017 All wt. loss first 260 hrs. 2 Zr; 4 Cb 446 0006 +0.4 mg. wt. change (consistent increase). 4 Zr; 4 Ch 446 0006 +0.3 mg. wt. change (no change first 260 hrs.). 2 Zr; 6 Ch 445 0004 +0.3 mg. wt. change (consistent increase). 2 Zr; 2 Oh 446 0008 All wt. loss first 90 hrs. 4 Zr; 2 Ch. 446 +.00016 +0.1 mg. wt. change. 6 Zr; 2 C 446 0005 All wt. loss during first 260 hrs. 2 Zr; 4 (lb 446 0007 +0.4 mg. wt. change. 4 Zr; 4; 0b.. 445 0005 Do. 2 Zr; 6 Ch. 445 0001 +0.1 mg. wt. change.

pH of H 5.65.*8. H.T.--High temperature. W.Q.Water quenched.

Norn.--In the foregoing tests, the asterisk indicates that the The remaining All samples were rinsed in distilled water and blown dry.

three minutes in (by Wt.) nitric acid solution. arttempt was made to clean them before weighing.

It will be apparent to those skilled in the art to which this invention pertains that various modifications can be made without departing from the preferred embodiments of this invention as disclosed herein, and thus it is not intended that the subject invention be limited other than by the scope of the appended claims.

What is claimed is:

.1. An alloy consisting substantially of uranium, zirconium, and columbium wherein the amount of uranium metal is greater than the total zirconium and columbium content and is the major constituent of the alloy.

2. An alloy consisting substantially of uranium as the predominant metal, zirconium and columbium wherein the total content of said minor alloying elements is between two and eight percent by weight.

3. A ternary alloy consisting substantially of a predominant amount of uranium metal and zirconium and columbum wherein the minor alloying elements columbium and zirconium are each present in amounts between 1 and 4 percent by weight.

4. An alloy consisting essentially of uranium metal, zirconium and between 1 and 4 percent by weight columbium, wherein said columbium is present in excess of the zirconium.

5. An alloy consisting essentially of uranium metal and a total content of columbium and zirconium between two and eight percent wherein said columbium and zirconium are each present in amounts between one and four percent by weight.

6. An alloy consisting essentially of uranium metal and zirconium and columbium as minor alloying elements wherein the total percent of said minor alloying elements is at least about two percent.

7. An alloy consisting essentially of uranium and a total of at least two percent minor alloying materials consisting of columbium and zirconium wherein the ratio of said columbium to zirconium is at least about 2 to 1, respectively.

8. A process for preparing an alloy of uranium comprising casting at a high temperature uranium alloy consisting substantially of uranium as the predominant metal corrosion product was removed by immersing for two to samples listed showed no reaction with nLtl'LC acid so no and a total of at least two percent of minor alloying elements, namely, columbium and zirconium, heat treating said alloy at an elevated temperature to obtain a homogeneous composition and subsequently quenching said homogeneous alloy composition.

9. The process of claim 12 wherein said alloy of uranium is subjected to prolonged heat treatment at a temperature of 1000 C. and subsequently quenched from a temperature of at least 725 C.

10. A process for preparing an alloy of uranium comprising adding the total minor alloying elements, columbium and zirconium, to uranium during the casting of said uranium, heat treating the alloy formed thereby at 1 000 C. and quenching said alloy mixture from a temperature of at least 725 C.

11. The process of claim 14 wherein said minor alloying elements are added in the approximate ratio of at least 2 parts columbium to 1 part zirconium in amounts sulficient to bring the total content of minor alloying elements to between two and eight percent by weight.

12. A process for preparing a corrosion-resistant alloy of uranium comprising adding columbium and zirconium, in amounts sufficient to bring the total content of minor alloying elements to between two and eight percent by weight, to uranium metal during the casting of said uranium metal, heat treating at 1000 C. the alloy formed thereby, and quenching said alloy mixture from a temperature of at least 725 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,237,872 Badger Apr. 8, 1941 FOREIGN PATENTS 114,150 Australia May 2, 1940 561,592 Great Britain May 25, 1944 OTHER REFERENCES Journal of the American Chemical Society, vol- 68, pages 242.1, 2 22 (1946) UNITED STATES PATENT oFFIQE CERTIFICATE OF CZQRRECTIQN Patent No 294L621 August 2, 1960 Frank G, Foote It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 34 for "Water" read watch column 6 line :28 for the claim reference numberal "12 read 8 lime 38 for the claim reference numeral "14" read l0 "-0 Sigried and sealed this 25th day of April 1961a (SEAL) Attelt:

ERNEST w SWIDER Attelting Oficer DAVID L, LADD 4 Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N09 2 94L7 62l August 2 1960 Frank G. Fooie It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 34 for "water" read watch column 6 line .28 for the claim reference numberal "12" read 8 lime 38 for the claim reference numeral "14" read 10 Signed and sealed this 25th day of April 1961.

(SEAL) Attelt:

ERNEST W. SWIDER DAVID L, LADD Attelting Oflicer Commissioner of Patents 

1. AN ALLOY CONSISTING SUBSTANTIALLY OF URANIUM, ZIRCONIUM, AND COLUMBIUM WHEREIN THE AMOUNT OF URANIUM METALS IS GREATER THAN THE TOTAL ZIRCONIUM AND COLUMBIUM CONTENT AND IS THE MAJOR CONSTITUENT OF THE ALLOY,
 8. A PROCESS FOR PREPARING AN ALLOY OF URANIUM COMPRISING CASTING AT A HIGH TEMPERATURE URANIUM ALLOY CONSISTING SUBSTANTIALLY OF URANIUM AS THE PREDOMINANT ELEAND A TOTAL OF AT LEAST TWO PERCENT OF MINOR ALLOYING ELEMENTS, NAMELY, COLUMBIUM AND ZIRCONIUM, HEAT TREATING SAID ALLOY AT AN ELEVATED TEMPERATURE TO OBTAIN A HOMOGENEOUS COMPOSITION AND SUBSEQUENTLY QUENCHING SAID HOMOGENEOUS ALLOY COMPOSITION. 